# Is there a MATLAB function that can compute the area of my patch?

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MathWorks Support Team 2012 年 2 月 8 日

I use the ISOSURFACE function to generate a patch object:
[x,y,z,v] = flow;
p = patch(isosurface(x,y,z,v,-3));
isonormals(x,y,z,v,p)
set(p,'FaceColor','red','EdgeColor','none');
daspect([1 1 1])
view(3);
camlight
lighting gouraud
I would like to find the area of the patch "p".

### 採用された回答

MathWorks Support Team 2019 年 8 月 29 日

There is no function which directly calculates the surface area of a patch object in MATLAB, however the calculations can be done in a fairly straightforward way using the 'Faces' and 'Vertices' properties of the patch object.
The surface area of the entire patch is then the sum of the areas of all the patch faces. The area of each triangular face can be computed with a cross product. Here is an example:
[x,y,z,v] = flow;
p = patch(isosurface(x,y,z,v,-3));
isonormals(x,y,z,v,p)
set(p,'FaceColor','red','EdgeColor','none');
daspect([1 1 1])
view(3);
camlight
lighting gouraud
verts = get(p, 'Vertices');
faces = get(p, 'Faces');
a = verts(faces(:, 2), :) - verts(faces(:, 1), :);
b = verts(faces(:, 3), :) - verts(faces(:, 1), :);
c = cross(a, b, 2);
area = 1/2 * sum(sqrt(sum(c.^2, 2)));
fprintf('\nThe surface area is %f\n\n', area);
If the patch object is constructed with faces that are not triangular (for example, they are rectangular), then each face can be broken down into triangular pieces (a rectangular face can be thought of as two triangular faces).
##### 4 件のコメント表示非表示 3 件の古いコメント
Uwe22 2017 年 6 月 16 日
Hej, I would like to extend this thread in order to ask if surface area of isosurfaces may also extend to compute the volume of total surfaces? Thank you.

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